INTRUSIVE LIMESTONES IN THE KESHYA AND MKWISI VALLEYS, NORTHERN RHODESIA

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Abstract
Two intrusive limestones in the valleys of the Keshya and Mkwisi streams, tributaries of the Kafue River, are described : the Keshya limestone, which intrudes the roof-migmatite zone of the Kafue Gorge granite, and the Mkwisi limestone, which intrudes a series of late Pre-Cambrian metasediments and contains xenoliths of similar granite. Brecciation of the country-rocks is extensive and the intrusions are irregular in form. Xenoliths are abundant in the limestones, which are coarse-grained, impure calcite-marbles with accessory magnetite, haematite, pyrite, apatite, rutile, monazite and xenotime. Alteration of the country-rocks is characterized by the introduction of alkali-feldspars, phlogopite and titanium minerals. The origin of the limestones is discussed and it is concluded that they represent an unusual type of carbonatite activity, resembling hydrothermal vein-like deposits in some of their characteristics but probably emplaced by a process of fluidization.